Visual indicating devices for use in aircraft



April 16, 1963 A. M. A. MAJENDIE VISUAL INDICATING DEVICES FOR USE INAIRCRAFT Filed Oct. 31, 1960 I5 Sheets-Sheet 1 AMA. MNBWE April 16, 1963A. M. A. MAJENDIE 3,085,429

VISUAL INDICATING DEVICES FOR USE IN AIRCRAFT Filed 001;. 31, 1960 3Sheets-Sheet 2 IrNim' R A .V\. A. Mmmmt:

April 16, 1963 A. M. A. MAJENDIE VISUAL INDICATING DEVICES FOR USE INAIRCRAFT Filed Oct. 51, 1960 3 Sheets-Sheet 3 AMA. Mmznmz O UJM UnitedStates Patent 3,085,429 VISUAL INDICATENG DEVICES FOR USE IN AIRCRAFTAlastair Michael Adair Majendie, Cookham Dean, England, assignor, bymesne assignments, to S. Smith 8: Sons (England) Ltd, London, England, acorporation of England Filed Oct. 31, 1960, Ser. No. 66,203 Claimspriority, application Great liritain Jan. 20, 1960 29 flaims. (Cl.73-178) The present invention relates to visual indicating devices foruse in aircraft and is concerned in particular with such devices whichare improvements in or modifications of those described and claimed inthe specification filed in respect of United States patent applicationSerial No. 758,970. The invention is also concerned with aircraftcontrol cabins which are improvements in or modi fications of thosedescribed and claimed in the said complete specification.

The invention is concerned in particular with the arrangement of thesevisual indicating devices in an aircraft control cabin for the purposeof imparting additional visual information to a pilot whilst he ismaintaining a continuous watch out of the aircraft through a windscreenprovided for that purpose, or in some instances whilst he is engaged inlooking at other devices within the control cabin. Whilst thisinformation may relate to any chosen quantities, the case in which theinformation relates to the control of the aircraft in pitch and in bankis a particularly important and useful one. The invention is alsoconcerned with the form of the indicating devices.

According to the present invention an aircraft control cabin in whichthere is a windscreen through which a pilot looks forwards from theaircraft in operation, is provided with a first visual indicating devicecapable of providing a moving optical stimulus in the form of one ormore light sources which may be made to move or appear to move along aline approximately parallel to said general direction, the line lyingwithin the periphery of the pilots field of view and to one side of hisline of sight when looking in said general direction, a second visualindicating device capable of providing a moving optical stimulus in theform of one or more light sources which may be made to move or to appearto move along a line lying transversely of said general direction, theline lying within the top or the bottom of the periphery of the pilotsfield of view when looking in said general direction, means foractuating the first visual indicating device to provide a moving opticalstimulus the rate and direction of which are indicative of the magnitudeand sense of any departure of a first quantity from a desired value andmeans for actuating the second visual indicating device to provide amoving optical stimulus, the rate and direction of which are indicativeof the magnitude and sense of any departure of a second quantity from adesired value. The general direction will usually be forwards from theaircraft and substantially parallel to its fore-and-aft axis.

Preferaby, the first visual indicating device is duplicated, theduplicate visual indicating devices lying one on either side of thepilots line of vision when looking in said general direction. The secondvisual indicating device may also be duplicated if required, theduplicate visual indicating devices lying one at the top and one at thebottom of the periphery of the pilots field of view when looking in saidgeneral direction. The visual indicating devices will usually bearranged so that the lines of movement are horizontal when the aircraftis in level flight. It will be appreciated, however, that they may lieonly approximately horizontal, for example at angles of to thehorizontal or more, and that in addition they may be slightly curved.Further, the first indicating device or devices need not be arranged sothat the lines of movement are exactly parallel to said generaldirection. They may be only approximately parallel to it, for example atangles up to about 20, and where there are two, they may, for exampleconverge away from the pilot at an angle to one another, for example anangle of 2040.

Where the second visual indicating device (or one of them if it isduplicated) lies at the bottom of the pilots field of view when lookingin said general direction, it will usually be arranged across the top ofhis instrument panel. The first visual indicating device or devices mayalso be at or near the same level and it is then possible for theindicating devices to serve their intended purpose whilst the pilot isobserving instruments on the panel, as they will still lie within theperiphery of his field of view.

One particularly important case is that in which the first and secondquantities are or are related to the aircrafts pitch and bank attitudesrespectively. In particular, the visual indicating devices may beactuated in dependence upon the magnitudes and senses of pitch and bankerror signals which are derived respectively from the differencesbetween demanded and actual pitch attitude signals and demanded andatual bank attitude signals. In these cases, the demanded pitch or bankattitude signals represent respectively the desired value of pitch orbank attitude. The demanded attitude signals may simply representdemands for a fixed datum attitude, commonly that for straight and levelflight, but they may be more complex and depend on two or more relatedvariables. For example, a pitch demand signal may be a combination of afirst signal demanding on its own a level pitch attitude and a secondsignal which demands the pitch attitude to be varied so that theaircraft climbs or descends to reach a predetermined height and thenlevels out to maintain that height. The first signal would be a constantsignal and the latter a signal which would initially take some suitablevalue if the aircraft is not at the predetermined height and thendecrease gradually to zero as the aircrafts height approaches thepredetermined value owing to the change in the aircrafts pitch attitudebrought about by the signal. Once the predetermined height is reached,the

second signal will vary only by small amounts on either side of zero ifthere is any tendency for the aircraft's height to change. At the sametime, the pitch attitude will be maintained level as determined by theconstant value of the first signal.

In another example, the bank demand signal may be a combination of aheading error signal derived from a compass and a signal representingthe lateral deviation of the aircraft from the centre of a radio-definedbeam. If the datum heading set in the compass is that of the beamdirection and we start with the aircraft on the correct heading butdisplaced from the beam centre, the first signal would be zero and thesecond at some value according to the displacement. This would cause theaircraft to be banked to turn in such a way as to decrease the lateraldisplacement and hence the second signal. Meanwhile, the first signalwould increase in the opposite sense as the heading deviated from thedatum and would eventually outweigh the second signal and cause theaircraft to be banked in the opposite direction so as to turn to bringit back towards the correct heading. The lateral displacement wouldstill be decreasing, however, and eventually the aircraft will have beenbrought on to the correct heading with no displacement from the beam.

vices is or are actuated so that the direction of move- 7,

ment of the optical stimulus is forwards when the pitch attitude differsfrom a desired one in such a manner that the aircrafts nose needs to bedepressed (ie the angle of dive increased or the angle of climbdecreased) and backwards when a manoeuvre in the opposite sense isrequired. Preferably, also, the second visual indicating device ordevices is or are actuated so that the direction of movement of themoving optical stimulus is to the left or to the right according as towhet-her the bank attitude differs from a desired one'in such a mannerthat the aircraft needsto be banked towards the left or towards theright respectively. The opposite senses of movement may also be used buthave been found in general to be less effective in operation.

According toa feature of the present invention, apparatus'for use in anaircraft control cabin according to the present invention, comprises atleast two visual indicating devices, each of which comprises acylindrical member mounted for rotation about its longitudinal axis andmeans for illuminating a continuous helical area of at least twocomplete'turnson the surface of the member, the member being mounted inan enclosure provided with a slot'exposing a longitudinal strip of thesurface of the member, actuating means for each device which meansincludes a motor coupled to the device to cause rotation of the memberabout its longitudinal axis in either sense and separate means forenergising each motor to drive the member at 'a'velo-city and in a sensedependent on the magnitude and sense of an input signal, and means forgenerating and applying to each said actuating means a signal dependenton the magnitude and sense of the varia-' tion of a variable quantityfrom a desired value.

Preferably the helical area consists of between four and ten completeturns. The cylindrical member may have interlaced black and whitehelices on its surface and be illuminated generally so that the whitehelix appears as "an illuminated helical area.

An example of an aircraft control cabin and apparatus for use thereinaccording to the present invention will now be described with referenceto the accompanying drawings in whichi FIGURE 1 shows a block schematicdiagram of the apparatus,

FIGURE 2 shows a view of one indicating device and FIGURE 3 shows a viewof part of the cabin with three indicating devices mounted in position.

The apparatus to be described and of which a block diagram is shown inFIGURE 1, includes three visual indicatingdevices 14 which :are showndiagrammatically in FIGURE 1" approximately as they appear in plan viewwhen arranged in an aircraft cockpit to provide indicaticns to a'pilotpositioned in the region of the point P. When looking ahead out of theaircraft, the pilot would look in the direction of the arrow shown inFIGURE 1 passing through the point P. The devices 1-3 lie horizontallyand their vertical level is approximately that of the top of theinstrument panel (bottom of the windscreen) so that they lie in thebottom of the pilots field of view when he is looking ahead out of thewindscreen, the device 1 lying transversely of the direction in which heis looking and the devices 2 and 3 approximately parallel to thatdirection.

The indicating devices 1-3: are represented only diagrammatically inFIGURE 1, each consisting of a cylindrical member which may convenientlybe between four and twelve inches in length and about three quarters ofan inch in diameter. The member had interlaced black and white helicespainted on its surface, the resultant black and white bands being halfan inch wide. The members are mounted for rotation about theirlongitudinal axes and each is contained within a case having a slotwhich allows a longitudinal strip of the surface of the member to beviewed from without. The width of the strip is about half the diameterof the members. The surfaces of the members are illuminated from withinthe cases and on rotation of a member the apparent effect to a personviewing through the slot is of a number of illuminated areas moving inone direction or the other along the length of the slot. The apparentdiroot-ion of motion depends on the direction of the rotation of themember and the speed is proportional to the speed of rotation.

FIGURE 2 of the drawings shows a perspective view of one of the devices,showing part of the surfaces of the cylindrical member 4 visible througha longitudinal slot 5 in the cylindrical case 6 within which the member4 is mounted. The case 6 is supported from a further casing 7 whichcontains an electric motor for driving the member 4 and other associatedequipment which will be described in more detail below.

. FIGURE 3' of the drawings shows a view from behind the pilots seat ofone side of the front of an aircraft cockpit, there being shown thepilots seat 3, the three indicating devices 1- 3, parts of thewindscreen 9 and of the instrument panel 10, and the control column 11.Where, as is usual in large transport aircraft, a co-pilots seat andcontrol column is provided, the devices 1-3 may be duplicated and theduplicate set being similarly arranged with respect to the co-pilot7sseat and the part of the windscreen 9 through which he normally looks.

Turning back to FIGURE 1, it will be seen that the cylindrical member ofeach device 13 is shown coupled to the output shaft of an electric motor15, 16 or 17. These motors 15 17 are mounted in the casings 7 (FIG- URE2), together with certain, associated apparatus used to assist in thecontrol of the motors. In the case of the device 1, this associatedcontrol apparatus includes a tachometer generator 16 driven by theoutput shaft of the motor 15 to generate a voltage proportional to thespeed of the motor 15, a servo amplifier 19 for controlling theoperationof the motor 15,, which amplifier may be of any desired form, forexample a thermionic valve or magnetic amplifier, and a signal combiningdevice 20 having two signal inputs and a single output which is coupledto the input of the amplifier v19. One of the inputs of thedevice, 2%)is coupled to the output of the tachometer generator 19 and theother toan input line Zll. As indicated by the plus and minus signs against theappropriate input leads to the device 20,the signals fed to it are insuch senses as to subtract from one another to provide a differencesignalfor application to the amplifier 19. This sign convent-ion is usedthroughout FIG- URE 1 in respectof the several signal combining devicesincluded in it.

By thus feeding back the output of the tachometer generator 18 to theinput of the, amplifier 19 in opposition to the signals on theline 21,the servo-control system for the device 1 constituted by the elements 15and 1840 operates to drive the device 1 at a speed proportional to themagnitude of the input signal appearing on the line 21.

The input signal on the line 211's a bank error signal which is obtainedby comparing signals representing the aircrafts bank attitude andsignals representing a demanded bank angle, the difference being used togenerate a signal for application to the line 21. As a result the speedof rotation of the cylindrical member in the device 1 willdepend on thisbank error signal and its sense on the direction of the bank error. Forreasons which will be explained, the sensing is made such that the areasof light seen through the slot '5 (FIGURE 2) move to the left or theright according as to whether the pilot is re7 quired to move thecontrol column to the left or the right respectively to correct theerror giving rise tothe signal concerned.

The bank error signal may be generated in any-desired.

5 in FIGURE 2, and coupled to them by external leads. As shown, theapparatus includes a conventional gyrovertical 25 having a pick-Eproviding an electrical signal on line 26 representing the air-craftsangle of bank. This is applied to one input of a signal combining device27. A bank demand signal is applied to a second input of the device 27over the line 28 in the opposite sense to the bank angle signal. Thisdemand signal is derived from the output of a further signal combiningdevice 29, the output of which is coupled to the line Z8 through aconventional limiting circuit 30, provided to prevent the bank demandsignal exceeding a predetermined safe limit.

The device 29 has two inputs, one coupled to a compass system 31 in theaircraft, for example a directional gyroscope monitored by a magneticreference device, arranged in known manner to provide a signal on theline 32 representing the deviation of the aircrafts heading from adesired course and the other coupled to a three position switch 32. Bymeans of the switch 32, the other input of the device 29 can be leftdisconnected or can be coupled to an output of either an I.L.S.(instrument landing system) localiser receiver 33 or a V.'O.R. (VHF.omni-range) receiver 34. The signals from these outputs of the receivers33 and 34 are those which represent the lateral displacement of theaircraft from a selected radio beam. It will be appreciated that otherforms of radio apparatus may be arranged for selection by the switch 32if desired and that the two shown are simply commonly used examples. Thesignals applied to the two inputs of the device 29 are sensed additivelyso as to provide a combined bank demand signal, for example representingthe aircrafts deviation from the course of a selected radio beam and itslateral displacement from the centre of that beam. Alternatively, anyother means of computing bank demand, which may or may not includecompass information, may be used.

The third input to the device 27 is coupled through a signal shapingcircuit 35 to an output from a rate gyro 36 arranged to generate asignal representing the aircrafts roll rate, the signal being applied tothe device 27 so as to subtract from the bank demand signal on the line28. The shaper 35 has a characteristic determined in known manner sothat the output signal from the gyro 36 is applied to the device 27 onlyif the aircrafts rate of roll exceeds a predetermined value. This valueis set so that for all ordinary manoeuvres no roll rate signal isapplied to the device 27, but so that, if a large bank demand signaloccurs, the roll rate signal resulting from the consequent applicationof a large bank angle acts to oppose the bank demand signal andeffectively prevents the pilot from over-banking, a fault whichotherwise tends to occur if a rapid movement suddenly appears on thedevice '1 due to a sudden demand for a large change of course, This mayor may not be necessary according to the characteristics of the aircraftin which the apparatus is fitted.

The output from the device 27 is finally passed through a furthershaping circuit 37 to the input line 21 of the control system for thedevice 1. --The output of the device 27, ignoring the occasional effectof the signals from the roll rate gyro 36, is a true bank error signalrepresenting the difference between the aircrafts bank angle and ademanded angle of bank. The shaper 37 has a characteristic such that thesignals passed through it are relatively attenuated if they are of smallamplitude, this provision being made to reduce the sensitivity of thedevice 1 to small error signals which may arise due to turbulence orsimilar factors.

The apparatus provided for actuating the two devices 2 and 3 is similarto that for the device 1. It is arranged so that the cylindrical membersare rotated together at a speed representing a pitch error signal, thesensing being such that the areas of illumination seen through the slotsappear to move forward or backwards 'according to whether the pilotneeds to move the control column forwards or backwards respectively tocorrect the pitch error giving rise to the indication. Each motor 16 and17 is energised by an amplifier 38 or 39 and drives a tachometergenerator 40 or 41 in addition to the cylindrical member of the device 2or 3. The inputs of the amplifiers 38 and 39 are coupled to the outputsof signal combining devices 42 and 43 respectively. In the case of thedevice 42, there are two inputs, one coupled to the output of thetachometer generator 40 and the other to the common input line 44 of thetwo servo-control systems (16, 38, 40 and 42) and (-17, 39, 41 and 43)for the devices 2 and 3. The device 43, however, has a third input whichis coupled to the rotor of a synchrotransformer 45 which rotor is drivenby the output shaft of the motor 17. The stator of the transformer 45 iscoupled to the stator of a synchro-transmitter 46, the rotor of which isenergised by a suitable alternating current voltage 46a and is driven bythe output shaft of the motor 16. The signal applied to the device 43from the transformer 45 will be an alternating current voltage (this maybe converted to some other form of signal if required, for example to aD.C. signal by a demodulator) representing the difference of thepositions of the output shafts of the motors 16 and 17. By feeding thissignal back to the input of the amplifier 39 through the device 43, therotation of the members in the devices 2 and 3 is controlled to beexactly equal.

The signal applied to the common input line 44 is a pitch error signalafter passage through a shaping circuit 47, similar to the shaper 37 inthe bank circuits, the pitch error signal being obtained from the outputof a signal combining device 48. One input of the device 48 is coupledto a pitch signal pick-off in a gyro vertical 49 (this may be the sameapparatus as the gyro vertical 35, the one gyro vertical being providedwith both pitch and bank pick-ofls in known manner), providing signalsrepresenting the aircrafts actual pitch attitude. This is opposed by apitch demand signal derived from the output of a further signalcombining device 50 through a limiter circuit '51, provided to preventthe application of a pitch demand signals greater than a predeterminedsafe limit.

The device 50 has two inputs, the signals applied to which are combinedadditively, one coupled to the output of a datum pitch attitude settingdevice 52 and the other coupled to a three position switch 53 by a line54. The switch 53 can be operated to leave the line 54 disconnected, orto connect it to a height error signal generator 55, or the output of anI.L.S. receiver 56 representing the deviation in the vertical plane ofthe aircraft from a predetermined glidepath. The generator 55 may forexample include in known manner a barometric pressure capsule and meansfor generating from the movements of the capsule an electric signalrepresenting the aircrafts deviation from a datum height which can beset by the pilot. It will be appreciated that the receiver 56 willusually be part of the same I.L.S. equipment as the receiver 33, the oneequipment operating to provide the two required output signals from theradio signals received by it from an I.L.S. localiser and glidepathtransmitters and also that the switches 32 and 53 may be ganged orinterlocked in some way to arrange that the two I.L.S. signals areutilised together and that such other combinations of positions of thetwo switches as are permissible provide sensible combinations of inputsto the respective signal channels.

Here, again, it will be seen that various other sources of signals maybe included, if desired, for use in generat ing the pitch error signalsin such a form as to give various modes of operation. For example, theremay be provided sources of signals representing departure of theindicated airspeed or the mach number from datum values, thesequantities then being controlled to the datum by variation of theaircrafts pitch' attitude in accordance with the indications ofthe-devices 2 and 3, or sources of signals. generated to-giveindications of the manoeuvres necessaryto control the aircraftspitchattitude to give a selected rate of descent or climb, or to indicate thepitch manoeuvers necessary tocontrol the aircraft in accordance with.I.L.S. or radio-altimeter signals to carry out the. flare phase of alanding according to a predetermined programme. Alternatively the pitcherror signal may be computed from glidepath deviation signals alone.

By arranging the devices 1-3 in the positions shown in FIGURE 3, themoving optical stimuli produced by them in response topitch and bankerror signals lie within the periphery of the field of view of the pilotwhen he is looking ahead through-the windscreen 9. It has been found, asdescribed inmy co-pending United States patentapplication Serial No.758,970, that it is possible for the pilot to maintain unimpaired hisnormal fixated view forwards throughthe windscreen and yet to take fullaccount of the indications of the devices 1-3, the moving stimuliacting, it is thought, on the extra-foveal regions of the eyes. The sameapplies if the pilot uses his fixated vision to observe the instrumentpanel and also if he looks in any other direction in the cabin such thatthedevice l and one or both of the devices 2 and 3 lie in or towards theperiphery of his field of view. Thus if the pilot elects to make alanding in bad visibility conditions by flying down an I.L.S. beam underthe control of signals derived from the I.L.S. receiver or receivers 33ing with the instrumental demands, and can select at will 7 the time totransfer control of the aircraft path from the instrumental demands tovisual flying without any awkw'ardhiatus.

It is not of course essential that the exact arrangement of the devices1-3 shown in FIGURE 3 should .always be followed and it will beappreciated in particular that the arrangement'may be altered. to suitthe layout of a particular cockpit. Assuming the main requirement is forthe pilot to be able to watch ahead whilst making use of theindications, the device 1 may be positioned above his forward line ofsight through the windscreen, for example as indicated at 1 in FIGURE 3,or an additional-bank error actuated device may be provided in thatposition.- The position across the top'of the instrument panel ispreferred, however, as it enables the devices 1-3 to be utilized whilstobserving the panel. The devices 2 and 3 may be positioned as requiredon either side of thepilotsline of view, and preferably at about thesame levelas-the device 1. One of the devices 2 and 3 could be omittedbut his found that in practice a symmetrical display is-preferable. Theyneed not be parallel to the pilots forward line-of sight and indeed mayconverge away from him at angles of as much as 30-40. Again the devices14 need not be exactly horizontal, although the divergence should not'bemorethan a few degrees.

By positioning the devices 1-3 horizontally, or approximately so, theadvantage is obtained that disturbance of the pilots vision due'toturbulence, this being mainly in the vertical direction, will not giverise to false indications from'the devices 1-3, the apparent movementsof which are horizontal or nearly so.

As mentioned previously, the sensing of the movements in. the device 1is preferably'made such that the direction of movement, to left orright, corresponds to the directionof movement of the control columnrequired to correct'the error giving rise to themovement. Similarly in'thecase of the devices 2 and 3, it is made such that the movementis-forwards or backwards according as to whether the control columnneeds to be moved forwards or backwards. This sensing may not at firstsight appear to be the most appropriate, the opposite seeming on paperto be more logical (e.g, a left movement of the column to correct aright movement in the device 1), but it has been found that the sensingdescribed is preferable in operation, the control column movementsrequired in response to given indications seeming instinctively correctto the majority of pilots. The opposite sensing may of course beemployed, if required, but the one described is preferred.

The interiors of the cases 6 (FIGURE 2) are provided with lights capableof illuminating the. parts of the surfaces of the cylindrical membersvisible through the slots 5. These lights are preferably provided with abrightness adjustment, for example a variable resistance connected inseries with the lamps across the leads for connecting them to avoltagesupply source, to enable the pilot to adjust the brightness ofthe indications according to the light conditions in the cockpit, forexample to enable him to dim them to a suitable level at night. Inaddition, the slots 5 may be provided with spring loaded shuttersarranged to be normally closed by the spring loading and provided withan electromagnetically operated mechanism to open them only onenergization of the devices. The control circuit for this lattermechanism may include various relay contacts controlled by relays whichare operated to open the contacts, thus allowing the shutters to close,should various fault conditions arise in the apparatus associated withthe devices. Such fault conditions may for example include failure ofpower supplies or failure of a radio receiver output when it is beingemployed as a signal source for operation of one or more of theindicating devices.

In an aircraft that is fitted with an autopilot, the indicating devices1-3 can be used to operate as an autopilot monitor, if they are operatedfrom signals derived from similar sources to those being used to supplysignals to the autopilot. If the indicating devices are operated from anindependent set of signal sources which are identical to and switched inaccordance with the switching of the signal sources provided for theautopilot, the indicating devices will operate whilst the autopilot isin operation to indicate whether the autopilot is in fact correctlycarrying out its intended functions as any error on the part of theautopilot will show as corresponding movements in the indicatingdevices. These movements, besides acting as a warning, also indicate theaction required to correct the autopilot error. This will hold whetherthe error arises in the autopilot itself or the signal sourcesassociated with'it, since the indicating devices are operated from anindependent set of signal sources. Should the devices be coupled to thesame signal sources as the autopilot, the device will operate as amonitor only of the autopilot servo-amplifier channels and would itselfgive erroneous'indications'if for example a fault arose in a gyrovertical apparatussupplying signals to both. However, thislimitingmonitoring function can also be useful, particularly 'as awarning of runway faults in the servo channels of the-autopilot and asimultaneous indication of the control action needed to correct theresult of the fault.

Another possibility which arises here is that the shutters of thedevices1-3 should be kept closed as long as the autopilot is functioningcorrectly, in those installations where independent monitoringarrangements are provided, so that any movementsoccuIringin-the devicesdue to a fault would not distract the pilot or mislead him intothinkingthat the autopilot had mal-functioned. The con- .trolcircuitsfor theshutters can then be combined with or actuated from thefault warning circuits provided in the monitoringarrangements so thatthe shutters ope-n immediately a fault arises in the autopilot. In sucha case the shutters are preferably arranged so that, when they areclosed, there is a small opening left through which direct observationof the moving members within can be made, to enable the pilot to checkthe correct working of the system and to control the brightness of theillumination.

One particular form of indicating device has been described withreference to FIGURES l3 but it will be appreciated that other forms ofdevice for providing a moving optical stimulus, both the rate anddirection of which can be varied, may be substituted for them. Theseother forms include those which represent only a minor variation in thatthe method of obtaining a helical area of illumination in or on thesurface of a cylindrical memher is changed. Thus, instead of painting orotherwise marking black and white or, if required, other colouredhelices on the surfaces of the members, the latter may be hollow andopaque and be illuminated from within, a helical slot being cut in thesurface of each member. Again the member may be transparent and beilluminated from within, having opaque helices on their externalsurfaces. Yet again the member may have helical areas which can beexcited to luminescence or electro-luminescence.

More radical changes are also possible, although the described devicesare at present preferred from the point of view of simplicity androbustness. Thus, as described in the specification of United Statespatent application Serial No. 758,970 with reference to FIGURES 1, 2 and4-7, each device may be a row of light sources which are sequentiallyenergised or are all energised, the row being moved longitudinally inthe required manner in the latter case.

While there have been described above what are presently believed to bethe preferred forms of the invention, variations thereof will be obviousto those skilled in the art and all such changes and variations whichfall within the spirit of the invention are intended to be covered bythe generic terms in the appended claims, which are variably worded tothat end.

I claim:

' 1. An aircraft control cabin in which there is a windscreen throughwhich a pilot looks in a general direction forwards from the aircraft inoperation, and which is provided with a first visual indicating devicecapable of providing a moving optical stimulus in the form of at leastone light source which may be made to move along a line approximatelyparallel to said general direction, the line lying within the peripheryof the pilots field of View and to one side of his line of sight whenlooking in said general direction, a second visual indicating devicecapable of providing a moving optical stimulus in the form of at leastone light source which may be made to move along a line lyingtransversely of said general direction, the line lying within the bottomof the periphery of the pilots field of view when looking in saidgeneral direction, means for actuating the first visual indicatingdevice to provide a moving optical stimulus the rate and direction ofmovement of which are indicative of the magnitude and sense of anydifference between the aircrafts actual pitch attitude and a demandedpitch attitude and means for actuating the second visual indicatingdevice to provide a moving optical stimulus the rate and direction ofmovement of which are indicative of the magnitude and sense of anydifference between the aircrafts actual bank attitude and a demandedbank attitude.

2. An aircraft control cabin according to claim 1 which further includesan instrument panel at least part of which lies below the windscreen andin which the second visual indicating device lies across the top of theinstrument panel whereby it lies in the top of the pilots field of viewwhen looking at said panel.

3. An aircraft control cabin according to claim 1 in which the visualindicating devices are mounted with the lines of movement disposedhorizontally when the aircraft is in level flight.

4. An aircraft control cabin according to claim 1 in which the actuatingmeans for the first visual indicating device operates to provide adirection of movement which is forwards when the aircrafts actual pitchattitude needs to be altered in the sense to bring the aircrafts nosedownwards to become equal to the demanded pitch attitude and theactuating means for the second visual indicating device operates toprovide a direction of movement which is the same as the direction inwhich the aircraft needs to be banked in order to make the actual bankattitude equal to the demanded bank attitude.

5. An aircraft control cabin according to claim 1 in which eachindicating device comprises a cylindrical member, means for radiatinglight from a continuous helical area on the surface of said memberhaving at least two complete turns and an enclosure for said memberhaving a slot exposing a longitudinal strip of the surface of saidmember so as to be visible to the pilot.

6. An aircraft control cabin in which there is a Windscreen throughwhich a pilot looks in a general direction forwards from the aircraft inoperation, and which is provided with a pair of first visual indicatingdevices each capable of providing a moving optical stimulus in the formof at least one light source which may be made to move along a lineapproximately parallel to said general direction, the lines lying withinthe periphery of the pilots field of view and one on each side of hisline of sight when looking in said general direction, a second visualindicating device capable of providing a moving optical stimulus in theform of at least one light source which may be made to move along a linelying transversely of said general direction, the line lying within thebottom of the periphery of the pilots field of view when looking in saidgeneral direction, means for actuating the first visual indicatingdevices together to provide a moving optical stimulus the rate anddirection of movement of which are indicative of the magnitude and senseof any difference between the aircrafts actual pitch attitude and ademanded pitch attitude and means for actuating the second visualindicating device to provide a moving optical stimulus the rate anddirection of movement of which are indicative of the magnitude and senseof any difference between the aircrafts actual bank attitude and ademanded bank attitude.

7. An aircraft control cabin according to claim 6 in which the lines ofmovement in the two first visual indicating devices converge away fromthe pilot.

8. An aircraft control cabin according to claim 6 in which the actuatingmeans for the two first visual indicating devices are synchronised sothat the moving optical stimuli produced by those devices are identical.

9. An aircraft control cabin according to claim 6 which further includesan instrument panel at least part of which lies below the windscreen andin which the second visual indicating device lies across the top of theinstrument panel whereby it lies in the top of the pilots field of viewwhen looking at said panel.

10. An aircraft control cabin according to claim 6 in which the visualindicating devices are mounted with the lines of movement disposedhorizontally when the aircraft is in level flight.

11. An aircraft control cabin according to claim 6 in which eachindicating device comprises a cylindrical member, means for radiatinglight from a continuous helical area on the surface of said memberhaving at least two complete turns and an enclosure for said memberhaving a slot exposing a longitudinal strip of the surface of saidmember so as to be visible to the pilot.

12. An aircraft control cabin in which there is a windscreen throughwhich a pilot looks in a general direction forwards from the aircraft inoperation, and which is provided with a pair of first visual indicatingdevices each capable of providing a moving optical stimulus in the formof at least one light source which may be made to move along a lineapproximately parallel to said general direction, the lines lying withinthe periphery of the pilots field of view and one on each side of hisline of sight when 1 1 looking in said general direction, a pair ofsecond visual indicating, devices each capable of providing a movingoptical stimulus in the form of at least" one light source which maybemade to move along a line lying transversely of said generaldirection, the lines lying within the bottom and the top respectively ofthe periphery of the pilots field of view when looking in said generaldirection, means for actuating the first visual'indicating devices toprovide a moving optical stimulus the rate and direction ofmovement' ofwhich are indicative of the magnitude and sense of any differencebetween the aircrafts actual pitch attitude and a demanded pitchattitude and means for actuating the second visual indicating devicestoprovidea moving optical stimulus the rate and direction of .rnovementof which 'are indicative of the magnitude and sense of any differencebetween the aircrafts actual bank attitude and a demanded bank attitude.

13. An aircraft control cabin according to claim 12 in which the linesof movement in the two first visual indicating devices converge awayfrom the pilot.

14. An aircraft control cabin according to claim 12 in whichtheactuating means for the two first visual indicating devices aresynchronised so that the moving optical I stimulus produced by saidfirst indicating devices are identical and the actuating means for thetwo second visual indicating devices are synchronised so that the movingoptical stimulus produced by said second visual indicating devices areidentical.

15. An aircraft control cabin according to claim 12 which furtherincludes an instrument panel at least part of which lies below thewindscreen and in which the lower one of the second visual indicatingdevices lies across the top of the instrument panel whereby it lies inthe top of the pilots field of'view when looking at said panel.

16. An aircraft control cabin according to claim 12 in which the visualindicating devices are mounted with the lines of movement disposedhorizontally when the aircraft is in level flight.

17. An aircraft control cabin'according'to-claim 12 in which eachindicating device comprises a cylindrical member, means for radiatinglight from a continuous helical area on the surface of said memberhaving at least two complete turns and an enclosure for said memberhaving a.slot exposing a longitudinal strip of the surface of saidmember so as to be visible to the pilot.

18. An aircraft control cabin in which there is a windscreen throughwhich a pilot looks in-a general direction forwards from the aircraft inoperation and which is provided with a pair of first visualindicatingdevices and asecond visual indicating device, each devicecomprising a cylindrical member mounted for rotation about itslongitudinal axis, means for radiating light from a continuous helicalarea of at least two complete turns on the surface of the member, avariable speed motor coupled to the cylindrical member to cause rotationthereof about said axis and an enclosure for said member provided with aslot through which a longitudinal strip of the surface of said member isvisible, the first indicating devices being mounted one on either sideof the pilotsline of sight when looking in said general directionthrough the windscreen and in the periphery of his field of view withthe longitudinal axes of the cylindrical members substantiallyhorizontal and at least approximately parallel to said general directionand the slots of the enclosures directed inwards towards said line ofsight and the second indicating device being mounted below the pilotsline of sight-when looking in said general direction through thewindscreen and in the'periphery of his field of view with thelongitudinal axis of the cylindrical member lyingsubstantiallyhorizontal and transversely of said line of sight and theslot of-the enclosure directed towards the pilot, means for actuatingthe first visual indicating devices to cause the motors to rotate thecylindrical members in opposite senses (as viewed by the pilot) at aspeed and in directions such that the apparent motion of the visibleparts of said helical areas is of a magnitude and in i2 a'directionrepresenting any difference between the aircrafts actual pitch attitudeandv a demanded pitch attitude and me'ansfor actuating the. secondvisual indicating device to cause the motor to rotate the cylindricalmember at a speed and ina direction such that the apparent motion of thevisibleparts of said helical area is of a magnitude and in adirectionrepresenting any difference between the aircrafts actualbankattitude'and a demanded bank attitude.

19. An aircraft control cabin according to claim 18 in which eachcylindrical member has interlaced black and white helices on its surfaceand the indicating devices further include means mounted within theenclosure for illuminating the surface of the cylindrical member.

20. An aircraft control cabin according to claim 18 in which said motorsare servo motors, each forming part of an electric servo control systemforming said actuating means and comprising a servo amplifier forcontrolling the motor to rotate at a speed and in a sense dependent uponthe magnitude and sense of an applied signal, a tachometer signalgenerator driven by the motor to generate a feed-back signalrepresenting the speed of rotation of the motor, and means for applyingto said amplifier both said feed-back signal and a signal representingany departure of the respective one of the first and second quantitiesfrom its desired value.

21. An aircraft control cabin according to claim 18 in which there-isfurther provided means for generating a bank error signal representingthe difference between a demanded bank attitude and the actual bankattitude of the aircraft and means for applying said bank error signalto control the actuating means for the second visual indicating devices.

22. An aircraft control cabin according to claim 21 in which said bankerror signal generating means comprises means for generatinga bankdemand signal, means for generating an actual bank attitude signal andmeans for subtracting said two signals to generate said bank errorsignal, said means for generating a bank demand signal including atleast one source of signals which source is operative in flight togenerate a signal varying in dependence-upon the-aircrafts course andposition and representing a demand for the bank manoeuvres required forthe aircraft toilyon a pre-selected path.

23. An aircraft control cabin according to claim 22 in which there areat least two of said sources of signals and which further includesswitching means for bringing aselected one of said sourcesinto'operation.

24. Anaircraft control cabin according to claim 18 in which there isfurther provided means for generating a pitch error signal representingthe difference between a demanded pitch attitude and the actual pitchattitude of the'aircraft and means for applying said pitch error signalto control the actuating means for the first visual indicating'devices.

25. An aircraft control cabin according to claim 24 in which said pitcherror signal generating means comprises means for generating a pitchdemand signal, means for generating an actual pitch attitude signal andmeans for subtracting said two signals to generate said pitch errorsignal, said means for generating a pitch demand signal including atleast 'one source of signals which source is operative in flight togenerate a signal varying in dependence upon the aircrafts height andpitch attitude and representing a'deinand for the pitch manoeuvresrequired for the aircraft to fly on a pre-selected path.

26. An aircraft control cabin as set forth in claim 25, comprising aplurality of said means for generating a pitch error signal andswitching means for connecting a selected one of said means intooperation.

27. Visual indicating apparatus for use in an aircraft control cabin andadapted to be mounted towards the periphery of an operators field ofView when looking in a general direction. out of the. aircraft toprovide stimulation of the 'parafoveal region of the operators eye andto convey information to the operator without directly focussed visualinspection, the apparatus comprising at least two visual indicatingdevices each of which includes a cylindrical member mounted for rotationabout its longitudinal axis and means for radiating light from acontinuous helical area of at least two complete turns on the surface ofthe member, the member being mounted in an enclosure provided with aslot exposing a longitudinal strip of the surface of the member,actuating means for each device which means includes an electric motorcoupled to the device to cause rotation of the member about itslongitudinal axis in either sense and separate means for energising eachmotor to drive the member at a velocity and in a sense dependent on themagnitude and sense of an input signal, means for generating andapplying to the actuating means for a first one of said devices a signalrepresenting the ditference between the aircrafts actual pitch attitudeand a demanded pitch attitude, and means for generating and applying tothe actuating means for a second one of said devices a signalrepresenting the difference between the aircrafts actual bank attitudeand a demanded bank attitude.

28. Visual indicating apparatus according to claim 27,

References (Iited in the file of this patent UNITED STATES PATENTS2,053,183 Crane et al. Sept. 1, 1936 2,23 8,718 De Florez et al Apr. 15,1941 2,448,023 Folland et al. Aug. 31, 1948 2,496,274 De Florez Feb. 7,1950 OTHER REFERENCES D. G. Aid et al.: Displaying IntegratedInstrumentation, pp. 68-70, Electronic Industries, July 1958, copy inDiv. 65.

John Tunstall: Pilot Aid Designed for Automatic Landing, pp. 83-84,Aviation Week, July 11, 1960, copy in Div. 36.

1. AN AIRCRAFT CONTROL CABIN IN WHICH THERE IS A WINDSCREEN THROUGHWHICH A PILOT LOOKS IN A GENERAL DIRECTION FORWARDS FROM THE AIRCRAFT INOPERATION, AND WHICH IS PROVIDED WITH A FIRST VISUAL INDICATING DEVICECAPABLE OF PROVIDING A MOVING OPTICAL STIMULUS IN THE FORM OF AT LEASTONE LIGHT SOURCE WHICH MAY BE MADE TO MOVE ALONG A LINE APPROXIMATELYPARALLEL TO SAID GENERAL DIRECTION, THE LINE LYING WITHIN THE PERIPHERYOF THE PILOT''S FIELD OF VIEW AND TO ONE SIDE OF HIS LINE OF SIGHT WHENLOOKING IN SAID GENERAL DIRECTION, A SECOND VISUAL INDICATING DEVICECAPABLE OF PROVIDING A MOVING OPTICAL STIMULUS IN THE FORM OF AT LEASTONE LIGHT SOURCE WHICH MAY BE MADE TO MOVE ALONG A LINE LYINGTRANSVERSELY OF SAID GENERAL DIRECTION, THE LINE LYING WITHIN THE BOTTOMOF THE PERIPHERY OF THE PILOT''S FIELD OF VIEW WHEN LOOKING IN SAIDGENERAL DIREC-